Ac corona discharger

ABSTRACT

This invention provides an AC corona discharger provided with a shield, a corona discharging member, an electrode opposed to said discharging member, and a high-voltage AC source. The discharger has a controlling device for controlling the ratio of positive and negative components of the voltage applied to the discharging member from the AC source.

United States Patent m1 m1 3,714,531

Takahashi 1451 Jan. 30, 1973 AC CORONA DISCHARGER [56] References Cited [75] Inventor: Shinkichi Takahashi, Tokyo, Japan UNITED STATES PATENTS [73] Assignee: Canon Kabushiki Kaisha, Tokyo, 2,879,395 3/1959 Walkup ..3l7/262 A Japan [22] Filed; June 23, 1971 Primary Examiner-William M. Shoop, Jr.

I Assistant ExaminerHarry E. Moose, Jr.

[21] Appl' 155876 Attorney-Ward, McElhannon, Brooks & Fitzpatrick [30] Foreign Application Priority Data [57] ABSTRACT June 26, I970 Japan ..45/56368 invention provides an corona discha ger provided with a shield, a corona discharging member, an

[52] US. Cl. ..3l7/262 A, 317/2 R electrode Opposed to Said discharging member, d a Ill-Cl g g AC Source The discharger has a [58] Field of Search ..3l7/262 A, 2 F; 323/7, 24;

307/146, 317; 250/495 ZC, 49.5 GC

trolling device for controlling the ratio of positive and negative components of the voltage applied to the discharging member from the AC source.

6 Claims, 4 Drawing Figures PATENTED JAN 3 0 I975 SHEET 10F 2 FIG. 4

PATENTEDJMIBO I975 3.714.531

- SHEET 2 OF 2 FIG. 3

, FIG. 2

AC CORONA DISCHARGER BACKGROUND OF THE INVENTION 1. Field of the Invention I This invention relates to corona dischargers and more particularly to corona dischargers of electrophotographic copying apparatus.

2. Description of the Prior Arts There are various types of conventional AC corona dischargers for discharging the surface of a sheet of paper which is charged with positive charge or negative charge. The distinctive character of such devices is that generally the negative element of discharge is larger in degree than the positive element of discharge. Accordingly, when a conventional AC corona discharger is used, the negative charge on the charged surface of photosensitive materials is likely to remain after it is discharged. Thus, many problems have been occured in the use of electrophotographic copying apparatus embodying such conventional devices.

There are various types of electrophotographic copying processes. Particularly, in the electrophotographic copying process which transfers the electrostatic latent image to transferring materials after the electrostatic latent images are formed on photosensitive materials or the images are developed, it can be said that the latent images remain and also the residual developing images are sustained owing to the residual latent images. Therefore, the residual developed images are not cleaned out or eliminated by a cleaning process and electrostatic latent images remain on the photosensitive material surfaces. Consequently, harmful influences are frequently effected during the image forming step in the electrophotographic copying process.

Ordinarily, a stack of photosensitive materials or transferring materials are waiting, in feeding position, for being fed into the copying apparatus, and at that time they are charged electrostatically. As a result of the phenomenon of electrostatics, photosensitive materials or transferring materials, similar to the case of the photosensitive materials for transferring images, are also influenced harmfully while they are treated in the image transferring or forming step of the electrophotographic copying process. Furthermore, due to the electrostatic phenomenon, two sheets of photosensitive materials or transferring materials are sometimes inconveniently fed at the same time; and, because the sheets of the materials maintain an excessive charge after the copying process of the sheets, it is often difficult and time consuming to put the sheets of photosensitive or transferring materials in order on a receiving tray. Another disadvantage is that operators are sometimes struck by an electric shock of the electrostatic charge.

Apparently, the discharging effects of the conventional AC corona discharges, that discharge as described above are not sufficient to discharge the charged surfaces of the materials or papers, and a residual negative element of the charge remains. In an electrophotographic copying apparatus employing an AC corona discharger in the forming step of electrostatic latent image as well, the conventional and prior art dischargers which are employed in the copying apparatus are not sufficient to eliminate the residual negative element of charge on the charged surfaces completely, so that foggy electrostatic latent images are obtained.

The problem of electrostatic charge is also important in other industrial fields, as for example in the fabrication of synthetic fibers and rubbers; in the printing field, where the effects of electrostatic charge on the flammable solution of rubber and gasoline contained in printing ink are important and bring about dangerous accidents; and in workshops of papers or plastics where dust particles inconveniently stick to each other by means of the effects of the electrostatic charge. In order to overcome the problems or difficulties of electrostatic charge, the conventional AC corona discharging devices have been used. But the prior art discharging devices have many disadvantages including poor discharging capacity and the failure to completely discharge the negative component of charge on the materials.

Summary of the Invention Therefore, a primary object of this invention is to provide an improved AC corona discharger which is adapted to discharge the charge on negative or positive charged surfaces of the photosensitive materials completely and ideally, without leaving a residual negative charge on the charged surfaces to be discharged.

- Another object of the invention is to provide an improved AC corona discharger having an electrically controlled circuit, which is adapted to discharge the electric charge on the photosensitive materials completely and ideally.

In accordance with the invention, the preferable embodiment of an AC corona'discharger permits a positive current of ordinary level and negative current of limited level to flow by means of the AC corona discharger. In another embodiment of this invention, additional positive current is added to the ordinary positive current, althoughno additional negative current is added to the ordinary negative current. Thus, according to the AC corona discharger of this invention, dischargings of the positive component and the negative component of corona discharge can be controlled.

BRIEF EXPLANATION OF THE DRAWING FIG. 1 is a diagrammatical view showing the current wave of a conventional AC corona discharger.

FIG. 2 is a perspective view showing an embodiment of the AC corona discharger according to this invention.

FIG. 3 is a diagrammatical view showing the current wave of the AC corona discharger according to this invention.

FIG. 4 is a perspective view showing another embodiment embodiment of the AC corona discharger of this invention.

' DESCRIPTION OF THE PREFERRED EMBODIMENT In the accompanying drawings and particularly with reference to FIG. 1, there is illustrated a shape of current wave of corona discharge which occurs in the conventional AC corona discharger. As to the diagrammatical view of current wave of AC corona discharge of the conventional AC corona discharger, the AC corona discharge occurs with constant voltage.

As shown clearly in the diagrammatical view of FIG. 1, dischargings of the positive element and negative element occur alternately and the magnitude of discharge of the positive element of the convention dischargers may be smaller than that of the negative element. Due to this fact, a charged surface cannot be discharged completely by means of prior art dischargers.

In order to eliminate these difficulties of discharging, the present invention provides an improved AC corona discharger as shown in FIG. 2. With reference to FIG. 2, reference numeral 2 shows a discharging electrode, 1 shows a corona discharger containing a shield 3, and 4 shows an opposing electrode which is arranged to oppose the discharging electrode 2, and on which the member 5 to be discharged is placed. A high voltage power source 6 has a lead connected to the discharging electrode 2 of the AC corona discharger, and another lead is connected to the shield 3 and the opposing electrode 4. A circuit element of this invention is provided in the lead connecting the power source 6 to the discharging electrode 2. The circuit element of this invention includes rectifiers 7, 8 and a resistance device 9, and they are arranged as shown in FIG. 2. When a positive component of current flows from the high voltage power source 6 to the discharging electrode 2, the current flows through the rectifier 7. When negative element of current flows to the high voltage power source 6 from the discharging electrode 2, that current flows through the rectifier 8 and resistance device 9. Accordingly, the AC corona discharger having the construction described above permits the limitation and control of the negative element of discharging. In this manner the positive and negative elements of discharging can be made equal, so that the complete discharge of the charged surface is accomplished and the difficulties or problems as described above are solved.

The resistance device 9 may be replaced with a variable resistance device to controll the degree of discharge at will.

In FIG. 4, which shows another embodiment of this invention, a primary coil 10 connected to an AC power source (not shown) and a secondary coil comprising a first coil 1 l and a second coil 12 are shown. The second coil 12 has a rectifier l3 and a capacitor 14, connected thereto as shown in FIG. 4. Thus, both the AC high voltage added to the first coil 11 and positive element of DC voltage produced by the second coil 12 are impressed on the corona discharger 2.

In consequence, the degree of positive and negative discharge becomes equal and the corona discharging condition is developed into the ideal condition shown in FIG. 3.

When the second coil 12 is replaced with a variable coil, it is possible to adapt to various conditions of operation. In the AC corona dischargers shown in FIG. 2 and 4, the shields 3 may be made by electrical conductive materials such as stainless steel or aluminum, or insulating materials such as porcelains, glasses and acrylic plastics. Also, it is possible that the body of the shields may be made of a conductive material and the surface member of the shield be made of insulating materials. As to the constructions of the shields, the side member 3' of the shield 3 is made of the materials above-mentioned and the top member 3" is made of electrically conductive translucent materials so as to make free the passing of light; or, alternatively, the top member 3" may be omitted. While a wire-type corona discharging member is shown, needle-type or platetype corona dischargers may be employed and ar ranged with a suitable gradient against the opposing electrode.

Thus, in accordance with this invention, the surfaces charged to positive or negative valves can be discharged, ideally and completely, to zero degree of electric potential. Accordingly, the photosensitive surfaces which are cleaned in the electrophotographic copying or transferring apparatus can be discharged completely, thus facilitating the cleaning step of the surfaces. Because the electrostatic latent image does not remain in the material at all, very clear copying images are obtained with the subsequent copying step. The stack of photosensitive materials or transferring materials disposed in feeding position, for being fed into the copying apparatus, are discharged electrostatically and completely. Thus, each sheet of the photosensitive or transferring materials is fed one by one, and then each sheet is placed on the receiving tray accurately and securely.

While certain forms of this invention have been shown for purposes of illustration, it is to be clearly understood that various modifications may be made without departing from the scope of the invention as set forth in the appended claims.

I claim:

1. An AC corona discharging device, comprising;

a shielding member;

a corona discharging member placed within said shielding member;

an opposing electrode mounted opposedly to said corona discharging member;

an AC high voltage source having a pair of output terminals; and

means for coupling said pair of high voltage source terminals respectively to said corona discharging member and said electrode, said coupling means including means for passing the positive component of the voltage from said AC high voltage source, and for partially decreasing only the negative component of the voltage imparted to said corona discharging member from said AC high voltage source.

2. An AC corona discharging device as defined in claim 1, wherein said means for decreasing said voltage includes a resistor.

3. An AC corona discharging device as set forth in claim 1, in which said coupling means includes a conductor connected between one of said source terminals and said opposing electrode, said means for decreasing only the negative component of the voltage being connected between the other said source terminal and said corona discharging member, wherein said means for decreasing only said negative component of the voltage comprises a first diode coupled between said other source terminal and said discharging member to pass the positive component of said voltage to said discharging member, and further comprises a series combination of a second diode and a resistor, saidseries combination being connected in parallel with said first diode, and said second diode being arranged to pass said negative voltage component.

4. An AC corona discharging device as defined in claim 1, wherein said opposing electrode is disposed below said discharging member, and wherein the upper portion of said shielding member is optically open.

5. In an AC corona discharging device including a shielding member, a corona discharging member placed within the shielding member, and an opposing electrode mounted opposedly to the corona discharging member, the improvement comprising:

an AC high voltage source including a transformer having a primary winding and first and second secondary windings, said first secondary winding having one end connected to said discharging member, and said second secondary winding having one end connected to said electrode; a diode claim 5, wherein said opposing electrode is disposed below said discharging member, and wherein the upper portion of said shielding member is optically open.

t l I 

1. An AC corona discharging device, comprising; a shielding member; a corona discharging member placed within said shielding member; an opposing electrode mounted opposedly to said corona discharging member; an AC high voltage source having a pair of output terminals; and means for coupling said pair of high voltage source terminals respectively to said corona discharging member and said electrode, said coupling means including means for passing the positive component of the voltage from said AC high voltage source, and for partially decreasing only the negative component of the voltage imparted to said corona discharging member from said AC high voltage source.
 1. An AC corona discharging device, comprising; a shielding member; a corona discharging member placed within said shielding member; an opposing electrode mounted opposedly to said corona discharging member; an AC high voltage source having a pair of output terminals; and means for coupling said pair of high voltage source terminals respectively to said corona discharging member and said electrode, said coupling means including means for passing the positive component of the voltage from said AC high voltage source, and for partially decreasing only the negative component of the voltage imparted to said corona discharging member from said AC high voltage source.
 2. An AC corona discharging device as defined in claim 1, wherein said means for decreasing said voltage includes a resistor.
 3. An AC corona discharging device as set forth in claim 1, in which said coupling means includes a conductor connected between one of said source terminals and said opposing electrode, said means for decreasing only the negative component of the voltage being connected between the other said source terminal and said corona discharging member, wherein said means for decreasing only said negative component of the voltage comprises a first diode coupled between said other source terminal and said discharging member to pass the positive component of said voltage to said discharging member, and further comprises a series combination of a second diode and a resistor, said series combination being connected in parallel with said first diode, and said second diode being arranged to pass said negative voltage component.
 4. An AC corona discharging device as defined in claim 1, wherein said opposing electrode is disposed below said discharging member, and wherein the upper portion of said shielding member is optically open.
 5. In an AC corona discharging device including a shielding member, a corona discharging member placed within the shielding member, and an opposing electrode mounted opposedly to the corona discharging member, the improvement comprising: an AC high voltage source including a transformer having a primary winding and first and second secondary windings, said first secondary winding having one end connected to said discharging member, and said second secondary winding having one end connected to said electrode; a diode connected between the other ends of said secondary windings with its cathode connected to said other end of said first secondary winding; and a capacitor electrically connected from said cathode to said discharging member, whereby the positive component of the AC voltage applied between said discharging member and said electrode is increased with respect to the negative component of the AC voltage applied therebetween. 